Mass flow controller

ABSTRACT

The invention presents a mass flow controller capable of supplying always stably at desired flow rate in spite of pressure fluctuations at either upstream side or downstream side of the mass flow controller. The invention is a mass flow controller having a flow rate control valve and a flow rate sensor, more specifically comprising a pressure control valve disposed at the upstream side of the flow rate control valve, a pressure sensor disposed between this pressure control valve and the flow rate control valve, and a controller for controlling the pressure control valve by feeding back the output of this pressure sensor.

TECHNICAL FIELD

The present invention relates to a mass flow controller. Moreparticularly it relates to a mass flow controller free from pressureeffects.

BACKGROUND ART

FIG. 4 is a diagram showing an example of semiconductor manufacturingline using a conventional mass flow controller. In FIG. 4, referencenumerals 11, 12 are chambers composing two systems of semiconductormanufacturing line, 13 a to 13 d are gas feed lines for feedingdifferent gases G₁, G₂ into chambers 11, 12, and 14, 15 are gascylinders for feeding gases G₁, G₂, respectively.

The gas feed lines 13 a to 13 d are composed of mechanical pressureregulators 16 a to 16 d, gauges 17 a to 17 d at the downstream side ofthe pressure regulators 16 a to 16 d, and mass flow controllers 18 a to18 d. Reference numerals 19 a to 19 d are filters. The gas feed lines 13a, 13 c supply gas G₁, into the chambers 11, 12, and the gas feed lines13 b, 13 d supply gas G₂ into the chambers 11, 12. That is, plural gasesG₁, G₂ are supplied into plural lines 13 a to 13 d.

The pressure of the gases G₁, G₂ supplied from the cylinders 14, 15 isusually reduced to about 98 kPa at the outlet side, and by furtherreducing to about 30 kPa, for example, by the pressure regulators 16 ato 16 d, the gases are supplied into the mass flow controllers 18 a to18 d, so that damage of mass flow controllers 18 a to 18 d may beprevented. The manager of semiconductor manufacturing line controls themass flow controllers 18 a to 18 d so as to supply gases G₁, G₂ atspecified flow rate in the chambers 11, 12, and adjusts the pressureregulators 16 a to 16 d while observing the gauges 17 a to 17 d, andtherefore adjusts properly the pressure of gases G₁, G₂ to be suppliedinto the mass flow controllers 18 a to 18 d.

As shown in FIG. 4, by combining the mass flow controllers 18 a to 18 dwith pressure regulators 16 a to 16 d, stable control is realized ifpressure fluctuates slightly at the supply side of gases G₁, G_(2.)

However, in the conventional combination of mass flow controllers 18 ato 18 d with the pressure regulators 16 a to 16 d, the plural members 16a to 16 d, 17 a to 17 d, 18 a to 18 d, and 19 a to 19 d must be linkedand coupled, it takes much time and cost in installation of gas feedlines 13 a to 13 d. Besides, the greater the number of pipings forconnecting the members 16 a to 16 d, 17 a to 17 d, 18 a to 18 d, and 19a to 19 d, the higher becomes the risk of gas leak and other problems atjunctions, and the resistance caused by piping may bring about limits inflow rate or unstable elements.

Only by flow control by combination of the mass flow controllers 18 a to18 d with the pressure regulators 16 a to 16 d, it was not alwayspossible to control the flow rate stably, in case of substantial changesin flow rate, due to fluctuations of inlet side pressure and outlet sidepressure of the flow rate control device in the mass flow controllers 18a to 18 d.

That is, while the flow rate is somewhat stable, the mechanical pressureregulators 16 a to 16 d can adjust the pressure appropriately, but itmay not be possible to follow when flow rate changes suddenly, andpressure fluctuations at the inlet side caused by sudden control of flowrate by the mass flow controllers 18 a to 18 d may cause instability incontrol of flow rate by the mass flow controllers 18 a to 18 d.

Besides, sudden changes in gas flow rate supplied by the gas feed line13 a may cause effects on the pressure at the upstream side of thepressure regulator 16 a, and it may also lead to disturbance in the flowrate of the gas supplied by other gas feed line 13 c branched off fromthis.

Further, as shown in FIG. 5, in order to reduce the cost, a plurality ofmass flow controllers 18 a to 18 d may be controlled by branching andconnecting pipes from the pressure regulators 16 a, 16 b, but in such acase, however, effects of pressure fluctuations becomes greater.

The invention is devised in the light of the above problems, and it ishence an object thereof to present a mass flow controller capable ofcontrolling always stably at setting flow rate in spite of pressurefluctuations at either upstream side or downstream side of the mass flowcontroller.

DISCLOSURE OF THE INVENTION

To achieve the object, the mass flow controller of the invention has aflow rate control valve and a flow rate sensor, more. specificallycomprising a pressure control valve disposed at the upstream side of theflow rate control valve, a pressure sensor disposed between thispressure control valve and the flow rate control valve, and a controllerfor controlling the pressure control valve by feeding back the output ofthis pressure sensor.

Therefore, by using this mass flow controller, if pressure fluctuationsoccur at its upstream side, such effects can be securely eliminated bythe pressure control valve controlled by feedback with the output of thepressure sensor, and pressure fluctuations occurring at the downstreamside of the mass flow controller can be securely eliminated by the flowrate control valve controlled by feedback with the output of the flowrate sensor.

That is, if pressure fluctuation occurs whether at the upstream side orat the downstream side of the mass flow controller, the flow rate can bealways controlled stably. In other words, since the mass flow controlleritself has a pressure adjusting function, and the inlet side pressure ofthe flow rate control valve can be always kept constant, and itsperformance can be opened up to the maximum extent. Hence, the flow rateaccuracy and stability may be enhanced.

In order to supply gas at stable flow rate, conventional mechanicalpressure regulators are not needed, and the structure of gas feed linecan be simplified, and the cost for construction of gas feed line can besaved. In addition, it is not necessary to link and couple pluralmembers, and it eliminates risk of gas leak due to formation ofunnecessary piping passages and connections, or reduction of pressuredue to passage resistance.

When the pressure sensor faces to the passage immediately before theflow rate sensor, the pressure sensor faces to the passage required inthe mass flow controller, and the mass flow controller can be formed ina compact design, and since the pressure sensor is provided in thepassage immediately before the flow rate sensor, a stable flow ratecontrol is realized by feedback control using this flow rate sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram showing an example of mass flow controller ofthe invention.

FIG. 2 is a diagram showing an example of measurement of flow ratecontrol by using the mass flow controller.

FIG. 3 is a diagram showing an example of semiconductor manufacturingline using the mass flow controller.

FIG. 4 is a diagram showing an example of semiconductor manufacturingline using a conventional mass flow controller.

FIG. 5 is a diagram showing other example of semiconductor manufacturingline using the conventional mass flow controller.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a block diagram showing an example of mass flow controller 1of the invention. This mass flow controller 1 comprises a passage block3 for forming a passage 2 for passing a fluid (in this example, thefluid is a gas, but the fluid is not limited to gas alone), a pressurecontrol valve 4 coupled to this passage block 3, a flow rate sensor 5, aflow rate control valve 6, two pressure sensors 7, a controller 8 forcontrolling the members 4 to 6, and a filter 9.

The passage 2 is formed to circulate through the passage block 3,consisting of first to third passages 2 a to 2 c. Piping joints 3 a, 3 bare provided at the upstream end of the first passage 2 a and downstreamend of the third passage 2 c, respectively. The passage 2 may be formedby drilling, casting or other method, and if the second passage 2 b isformed by drilling, the passage block 3 must be separated at least atone position, but anyway by forming the passage blocks 3, 3 a, 3 bintegrally on the whole, gas leak can be prevented.

The pressure control valve 4 is composed of a diaphragm 4 a abuttingagainst a valve seat 3 c formed, for example, at one side of the passageblock 3, and its actuator 4 b, and the opening degree for linking andcoupling the passages 2 a, 2 b is controlled by a control signal Cp.

The flow rate sensor 5 is composed of a straightening element 5 ainserted, for example, in the second passage 2 b, a branch passage 5 bfor branching a specified flow rate 1/A from the second passage 2 b, anda sensor main body 5 c provided in this branch passage 5 b, and issues apassage signal Sf showing the total flow rate F.

The flow rate control valve 6 is composed of a diaphragm 6 a abuttingagainst a valve seat 3 d formed, for example, at one side of the passageblock 3, and its actuator 6 b, and the opening degree for linking andcoupling the passages 2 b, 2 c is controlled by a control signal Cf.

The pressure control valve 4, flow rate sensor 5, and flow rate controlvalve 6 are aligned at one side (upper side) of the passage block 3, andhence the overall size of the mass flow controller is suppressed.

The pressure sensor 7 is composed of a first sensor 7 a disposed at aside of the passage block 3 so as to face to the first passage 2 a, anda second sensor 7 b disposed at a side of the passage block 3 so as toface to the second passage 2 b, and the both pressure sensors 7 a, 7 bare buried in the passage block 3 in the different side of the side ofmounting the members 4 and 5 (in this embodiment, in FIG. 1, before thefirst passage 2 a and inside of the second passage positionedimmediately before the straightening element 5 a composing the flow ratesensor 5). Hence, the pressure sensor 7 can be installed withoutincreasing the overall size of the mass flow controller 1. The sensors 7a, 7 b issue pressure signals Spa, Spb showing pressures P₁, Pc in thefirst passage 2 a and second passage 2 b, respectively.

In this embodiment, the sensors 7 a, 7 b are provided at the side of thepassage block 3, but the mounting side is not particularly specified asfar as the pressure sensor 7 faces to the passage 2. That is, they maybe buried in the lower side of the passage block 3, or in the upperside, at any position not disturbing the control valve 4, flow ratesensor 5, or flow rate control valve 6.

The controller 8 consists of a control unit 8 b for feeding backpressure signals Spa, Spb (outputs) from the pressure sensor 7, issuinga pressure control signal Cp, and controlling the pressure control valve4 by feedback, a control unit 8 a for feeding back flow rate signal Sffrom the flow rate sensor 5, issuing a flow rate control signal Cf, andcontrolling the flow rate control valve 6 by feedback, and an interface8 c with outside. The control unit 8 a controls the flow rate controlvalve 6 by feedback according to a signal from outside, and also issuesa control signal to the control unit 8 b to control the pressure Pcimmediately before the straightening element 5 a at a specifiedpressure.

Although not shown in the drawing, the controller 8 has a display unitfor showing set values of flow rate F or provisional pressure Pc, orvalues P₁, Pc, F measured by sensors 5, 7 a, 7 b. The values P₁, Pc, Fmeasured by sensors 5, 7 a, 7 b can be issued outside through theinterface 8 c. The interface 8 c may be either digital communicationmeans or analog input and output means.

In this embodiment, in order to clarify the control relation, thecontrol units 8 a, 8 b are shown separately, but the invention is notlimited to this structure, and the entire mechanism may be supervisedand controlled by one controller 8 and the manufacturing cost may belowered.

In addition, control of pressure control valve 4 by the control unit 8 bis not limited to feedback control by using only the output signal Spbfrom the pressure sensor 7 b, and it may be controlled by using outputsignal Spa from the pressure sensor 7 a. By using the pressure sensor 7a as in this example, the pressure of the gas supplied in the mass flowcontroller 1 can be monitored, but this pressure sensor 7 a may be alsoomitted.

In the mass flow controller 1 of the invention, the control unit 8 bcontrols the pressure control valve 4 by feedback to a specifiedpressure Pc by using the pressure signal Spb from the pressure sensor 7b, and therefore if the inlet side pressure P₁ of the mass flowcontroller 1 fluctuates due to some effects, the mass flow controller 1can control stably. Besides, since the control unit 8 a controls theflow rate control valve 6 by feedback so that the measured flow rate Fmay conform to the preset flow rate Fs by using the flow rate signal Sffrom the flow rate sensor 5, and therefore if the outlet side pressureP₂ of the mass flow controller 1 fluctuates, it is free from itseffects.

Therefore, unlike the prior art, the mass flow controller 1 of theinvention does not require pressure regulators 16 a to 16 d in itsup-stream. Since the mass flow controller 1 of the embodiment alsoincorporates the filter 9, it is not required to link and couple filters19 a to 19 d separately as needed in the prior art. As a result, the gasfeed line is simplified, and the mounting footprint is saved. In thisembodiment, the filter 9 is disposed at the utmost upstream side of thepassage 2, but the invention is not intended to specify the position ofthe filter 9. As the case may be, the filter 9 may be omitted.

In particular, in the embodiment, the pressure sensor 7 b faces to thepassage 2 b immediately before the flow rate sensor 5 in the integratedpassage block 3, and the predetermined pressure Pc can be kept by usingthe pressure signal Spb of the pressure sensor 7 b; therefore, the flowrate F in a state that the pressure Pc is constant can be measuredcorrectly by the flow rate sensor 5.

Also, in the embodiment, the pressure control valve 4 and flow ratesensor 5 are arranged side by side, and the second passage 2 b disposedbetween them is designed as short as possible, and hence the time delayof pressure Pc with respect to the output of the opening degree controlsignal Cp of the pressure control valve 4 is minimized, and fluctuationsof pressure Pc in the section of the flow rate sensor 5 are made assmall as possible.

Further, in the second passage 2 b between the pressure control valve 4and flow rate sensor 5, the pressure sensor 7 b is disposed at aposition as close to the flow rate sensor 5 as possible (the passagecomposed immediately before), so that a pressure Pc having less effectsof disturbance or the like can be measured. As a result, the controlaccuracy and stability of flow rate by the mass flow controller 1 can beenhanced.

In addition, by eliminating fitting and piping from the second passage 2b between the pressure control valve 4 and flow rate sensor 5, it isfree from risk of pressure drop due to passage resistance or gas leak.

FIG. 2 is an example of measurement of pressure P₁ at upstream side ofmass flow controller 1, flow rate set value Fs, flow rate F determinedfrom output signal Sf of flow rate sensor 5, and control signals Cp, Cfwhen pressure P₂ is varied at downstream side.

In FIG. 2, the axis of abscissas denotes the time (seconds), andpressures P₁, P₂ are varied at random in every about 5 seconds, and inthis example, for example, the upstream side pressure P₁ is changedsuddenly in a range of 200±50 kPa, and the downstream side pressure P₂is changed suddenly in a range of 0 to 3.8 kPa.

As shown in FIG. 2, the control signal Cp changes by following thevariation of the upstream side pressure P₁ of the mass flow controller1, and hence the pressure Pc is kept constant in the second passage 2 binstalling the pressure sensor 7 b. The control signal Cf changes byfollowing the variation of the downstream side pressure P₂ of the massflow controller 1, and hence the flow rate F flowing in the flow ratesensor 5 is kept constant.

Herein, comparing the actually flowing flow rate F and the set value Fsof flow rate, the actual flow rate F varies slightly at the moment ofsudden changes in the pressures P₁, P₂, but the width of variation isvery slight, and it returns to the set value Fs immediately in a veryshort time.

That is, by using the mass flow controller 1 of the invention, if suddenpressure fluctuations occur whether at the upstream side pressure P ₁ orat downstream side pressure P₂, a specified flow rate continues to flowalways by a very stable control.

FIG. 3 shows an example of forming a semiconductor manufacturing line inthe same configuration as in the prior art shown in FIG. 4 by using thesame mass flow controller 1. In FIG. 3, the same reference numerals asin FIG. 4 represent the same parts and detailed description is omitted.

In FIG. 3, reference numerals 1 a to 1 d are mass flow controller 1 ofthe invention. That is, by using the mass flow controller 1 of theinvention, the gas feed lines 13 a to 13 d can be composed in a verysimple structure, and the time and labor for building the gas feed lines13 a to 13 d can be saved. At the same time, only a small area isrequired for installing the gas feed lines 13 a to 13 d.

INDUSTRIAL APPLICABILITY

Linking and coupling points of piping in gas feed lines 13 a to 13 d arevery few, and the risk of gas leak or other troubles can be reduced.

As explained herein, according to the invention, the flow rate can becontrolled at high precision and in a simple operation, without effectsof pressure fluctuations at the upstream side and downstream side.Besides, since pressure regulators are not required in the stage beforethe mass flow controller, the cost performance can be enhancedsubstantially.

1. A mass flow controller, which has a flow rate control valve and aflow rate sensor, characterized by comprising a pressure control valvedisposed at the upstream side of the flow rate control valve, a pressuresensor disposed between this pressure control valve and the flow ratecontrol valve, and a controller for controlling the pressure controlvalve by feeding back the output of this pressure sensor.
 2. The massflow controller according to claim 1, wherein the pressure sensor facesto the passage immediately before the flow rate sensor.
 3. A mass flowcontroller module that can control fluid flow and be installed as aunitary component, comprising: a housing block member having a fluidpassageway, mounted on the housing block member from an upstreamposition is a pressure control valve unit, a flow rate sensor unit and aflow rate control valve unit; a pressure sensor unit operatively mountedin the fluid passageway; and a control unit operatively connected to thepressure control valve unit, the flow rate sensor unit, the flow ratecontrol valve unit and the pressure sensor unit whereby the control unitcan automatically set and maintain a constant flow rate despite changesin fluid pressure.
 4. The mass flow controller module of claim 3 whereina second pressure sensor unit is mounted between the pressure controlvalve and the flow rate sensor and operatively connected to the controlunit.
 5. The mass flow controller module of claim 3 wherein the pressurecontrol valve unit, flow rate sensor unit and flow rate control valveunit are respectively mounted adjacent each other on fluid openings onthe housing block member including a pressure control valve seat and aflow rate control valve seat.
 6. The mass flow controller module ofclaim 3 further including a filter member mounted in the housing blockmember fluid passageway upstream of the pressure control valve unit. 7.The mass flow controller module of claim 3 wherein the housing blockmember has a non-linear fluid passageway with openings to the passagewayon an upper surface, the openings including a first annular valve seatfor operatively interfacing with a diaphragm member of the pressurecontrol valve unit, a pair of ports for connection to the flow ratesensor unit and a second annular valve seat for operatively interfacingwith a diaphragm member of the flow rate control valve.
 8. The mass flowcontroller module of claim 7 wherein the openings to the fluidpassageway are aligned in a row adjacent each other across the housingblock member.
 9. In a semiconductor production assembly utilizing asource of fluid, the improvement of a mass flow controller module thatcan control fluid flow and be installed as a unitary component,comprising: a housing block member having a fluid passageway connectedto the source of fluid, mounted on the housing block member from anupstream position is a pressure control valve unit, a flow rate sensorunit and a flow rate control valve unit; a pressure sensor unitoperatively mounted in the fluid passageway; and a control unitoperatively connected to the pressure control valve unit, the flow ratesensor unit, the flow rate control valve unit and the pressure sensorunit whereby the control unit can automatically set and maintain aconstant flow rate despite changes in fluid pressure.
 10. Thesemiconductor assembly of claim 9 wherein a second pressure sensor unitis mounted between the pressure control valve and the flow rate sensorand operatively connected to the control unit.
 11. The semiconductorassembly of claim 9 wherein the pressure control valve unit, flow ratesensor unit and flow rate control valve unit are respectively mountedadjacent each other on fluid openings on the housing block memberincluding a pressure control valve seat and a flow rate control valveseat.
 12. The semiconductor assembly of claim 9 further including afilter member mounted in the housing block member fluid passagewayupstream of the pressure control valve unit.
 13. The semiconductorassembly of claim 9 wherein the housing block member has a non-linearfluid passageway with openings to the passageway on an upper surface,the openings including a first annular valve seat for operativelyinterfacing with a diaphragm member of the pressure control valve unit,a pair of ports for connection to the flow rate sensor unit and a secondannular valve seat for operatively interfacing with a diaphragm memberof the flow rate control valve.
 14. The semiconductor assembly of claim9 wherein the openings to the fluid passageway are aligned in a rowadjacent each other across the housing block member.